This patent claims the benefit of U.S. Ser. No. 60/713,083 filed Aug. 31, 2005, which is hereby incorporated by reference.
An image sensor provides a grid of pixels, such as photosensitive diodes or photodiodes, reset transistors, source follower transistors, pinned layer photodiodes, and/or transfer transistors for recording an intensity or brightness of light on the diode. The pixel responds to the light by accumulating a charge—the more light, the higher the charge. The charge can then be used by another circuit so that a color and brightness can be used for a suitable application, such as a digital camera. Common types of pixel grids include a charge-coupled device (CCD) or complimentary metal oxide semiconductor (CMOS) image sensor.
The light received by a pixel is often based on the three primary colors: red, green, and blue (RGB). With these three primary colors, additional colors can be identified and/or created with various combinations and intensities (e.g., when red and green overlap they form yellow). However, it is generally noted that pixel sensitivity for blue light is innately worse than green and red light.
This problem is exacerbated in deep sub-micron technology. For example, it is often desired in deep sub-micron technology to utilize a silicon nitride or oxynitride layer to act as a borderless etch-stop layer. However, such a layer causes destructive interference because of the refractive index difference between different films. The difference of refractive index in such film stack will seriously degrade the photo response of the sensor, especially for blue light.
What is needed is a method and device for making a sensor with an improved response for all colors, including blue light.